Protective system for motors



Aug.A 2. 1927.

W. H. SMITH PROTECTIVE SYSTEM .Fon MoToRs Filed June 1. 1925 v ATTORNEY Patented Aug. 2, 1927'.r

UNITED .STATES g 1,637,356 PATENT OFFICE.

WALTER II. SMITH, OF WILKINSBURG, PENNSYLVANIA, ASSIQNOR TO WESTINGrHOUSE` ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

PROTECTIVE SYSTEM FOR MOTORS.

Application filed `Tune 1, 1925. Serial No. 34,066.V

t The object of the invention, generally stated, is the Vprovision of a. control system` for motor-generator sets that shall be sirnple and positive in operation and economically manufactured vand installed.

A more specific obyect of the invention 1s to insure the rotation of a motor-generator set at the proper pull-in speed, before the closing of the motor circuits.

A further object of the invention is to provide for the automatic closure ot the motor circuitsv when the motor reaches a predetermined pull-in speed.

Other objects of the invention'will inrpart be obvious and in part appear hereinafter.

The invention, accordingly, is disclosed in the embodiment thereof shown in the accompanying drawing and comprises the combination ot elements and arrangement of parts that will be exemplified in the system hereinafter set forth and the scope ot which Will be indicated in the claims.

For a fuller understanding ot the nature and objects of the invention, reference should be had to the following detailed description taken in connection With the accompanying drawing, Which is a. diagrammatic viewrof a control system arranged in accordance with this invention.

Referring now `tothe drawing, motorgenerator set is shown generally at 10. As illust-rated, the generator 11 mechanically connected to the motor 12v in any suitable manner, such, for example, as by the provision of a common shaft'. V

During operation, the motor 12 is supplied from any suitable source oi alternating-ciurent power through the main supply conductors 13. Preferably, these conductors 1S lead from a transformer that is mounted on the vehicle and energized through a pantograph that contacts with the main trolley conductor. y

It Will be readily understood, that it the motor 12, while at rest. is connected across the main supply conductors, it Will take a heavy current, which, iT" continued for any considerable length of time, may greatly damage the windings. Consequently, it is desirable to rotate the motor at some predevgenerator ,11 operated as a motor.

, motor termined speed at which it will build up, when connected across the line, a counter electromotive force suiiicientto prevent the flow ol' an excessive current. I

In the embodiment illustrated, one terminal of the motor 12 is connected to one of the supply conductors 13, through a blade of artwo-pole switch 14, which hereinafter Will be called the motor-generator switch, in order to distinguish it from other switches. The otherterminal of the motor is connected to t-he other supply conductor through a, contactinember V of a relay `switch shown generally at 16.

As Will be observed, the relay 16 comprises a series coil 19 and a shunt coilv21, which are mounted on a common core 22 andhave their adjacent terminals connected. The movable contact member 20 is pivotally mounted and disposed `for actuation to its closed position through the energization ot the, coils 19 and 21. Another contact member 223 is mounted in alinement with an arm 25, which is carried by the contact member 20 and is normally retained closed by a spring 24.

Since the contact member 20 is connected in the circuit of the motor. 10, the motor cannot be `connected across the line until the coils 19 and 21 are sufficiently energized to close the contact member 20. Consequently, by connecting the coils 19 and 21 for ditfern ential action, when the motor 12 is rotated by the generator 11, as will be explained hereinafter, the resultant energization of the coils may be varied directly as the speed and the counter-electromotive torceV of the Therefore, as Will be readily understood, the motor circuitmay be kept open until the reaches a predetern'iined pull-in speed. t Y Y In order to rotate the motor 12 to build up a counter electromotive force when connected across the line, the generator 11 is connected across any suitable source of electrical energy'and operated as a motor. `The power source used in this case is a storage battery 17 ot' the type usually provided onr electrically-operated motor vehicles Jfor supplying lighting systems and the like.

Asshown, the negative pole of the battery 17 is connected t-o the negative terminal of the generator through one blade ot the `motor-generator switch 14. The connection between the positive pole of the battery and the positive terminal of the generator is through the series coil 19 and is controlled by a contacter 18. Y

The contaetor 18 is of a well-known typeKV and comprises a contact plate that is disposed to bridge the contact fingers 31 upon the energization of a coil 30. In this system, the coil of the contactor is arranged for connection across the supply con ductors 13 by the closing of the motor-gen-y erator switci 14. Further description of this contacter 18 is considered unnecessary,'

since it is of a well-known type and is not a part of this invention.

One of the contact fingers 31, which are bridged bythecontact plate 20 when coil 30 is energized to close switch 18, is connected through conductor 32 to the positive conductor of train line 28 and the adjacent contact finger is connected to the positive terminal of the battery 17 through conductor 83 and one blade of a two-pole battery switch 15. Another of the contact'ngers 31 is'connectel through conductor 27 to the junction-point of the series and shunt coils 19 and 21,'respeetively.

Accordingly, upon closing the motor-generatorswitch 14 and the battery switch 15,

" the contacter 18 is actuated and a circuit is established from the positive terminal of the battery through battery switch 15, conductor 33, contact fingers 31, which are bridged by the plate 20, where the circuit divides, one branch including coil 19 of the relay 16, generator 11 and thence to the negative terininal of the battery through one blade ot the motor-generator switch 14. Thus, the

generator 11 is initially connected across the Y are rwound in the. same direction ou the core 2Q. Consequently, when vthe coils are energized from a common conductorQT connected to their point of juncture, the. current flowing in the coils passes in opposite diret-- tions about the core 22, lgiving a diliereutial magnetizing action. The coils are so proportioned that upon the initial .energizatiom they are nearly balanced. Ilowevcr, the geuerator 11, when operated a motor, builds up a countcr-electrolnotive torce tending to reduce the fiow ot' current in the series coil.

As the speed of the generator operating as a motor is increased, the counter-electromotive force developed further decreases the flow of current throu h the series coil 19,

`.thereby unbalancing t ie magnetizing effect of the series and shunt coils. Finally, i'l the voltage of the vbattery is sufficient to drive the generator, operating as a motor, at a speed great enough to develop a counterelectromotive force that ncutralizes the magnetizing etlect of the coil 19, then the shunt coil, being unopposed, causes a sufficient inagnetization ot the core to efi'ect closure of the relay 1G.

When the motor 12is rotated at proper pull-in speed and connected across the main source of" supply by the closure of relay 16, the counter-electroznotive force immediately generated will prevent the flow of an excessive current. Further, the above-described eircuits provide means `for preventing connection' of' the motor 12 across the main source of supply until it is rotating at the required pull-in speed, thereby requiring a minimum expenditure of energy by the battery 15.7, since the motorilQis not operated as a generator.

As will be observed, the resistor 26 is short-circuited by the Contact member Q3 when the latter is in its closed position. Consequently, when the relay 16 is operated to close the motor circuit, the contact member 23 is actuated by means of the arm 25 and the resistance unit .26 is connected in series relation with the shunt coil 21. In such manner, the current flowing through the shunt coil may be reduced as desired.

The shunt coil 21 and series coil 19 'are now energized from the generator 11,'which is operated bythe motor 12. Currentflows from the positive terminal of the generator through the series coil. 19,4V conductor 27, contactor 18, one blade ot lthe knife switch 15, through the battery 17, one blade ot' the motor-generator switch r14 and thence to the lgenerator. Another circuit is established from the generator through the series coil 19, shunt coil 21, resistance unit 2G and thence to the negative terminal of the generator 11.

Thus, it will be seen that the coils 19 and 2l are cun'uilative in Venergizing the core 22 when the generator 11 is driven by the motor and that current continues to flow in the saine direction through the shunt coil. Ac cordiugly, the relay 1h retained closed.

A control system of this type is adapted for multiple-unit operation of motor vehicles and by providing train lines 28 with suitable jumpers 29, any number of cars may be concurrently controlled. As shown, the negative terminal oi each battery is connected ,through one blade ot the battery switch 15 tothe negative conductor of the `train line 28. The positive conductor ot' the train line is connected through a conductor 32 to the contact fingers 31 of the contactor 18.

llt]

Vhen a plurality of cars are connected together as set forth above, and the battery and motor-generator switches on 'each vehi-v battery switch are both closed yand theV coil thus energized. In 'the manner set forth above, the coil 30 effects the operationl of the contactor 18 and the generator 11 is connected across the battery 17. Vhen the generator 11, operating as a motor, rotates at the predetermined pull-in speed the relay 16 functions to Aclose the motor circuit. The generator 11 is then driven by the motor 12 and charges the battery 17.

If the voltage of the battery or batteries is not sufficient to effect Athe rotation of the motor-generator set at the predetermined pull-in speed, it is impossible to operate the relay contact member 2O and thus the motor circuits cannot beolosed. This requires the operator to have the battery charged and so protects the motor-generator set.

Since various changes may be made in the abovedescribed construction and ar-V rangement o't parts and different embodiments of the invention may be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accom panying drawing shall be interpreted as illustrative and not in a. limiting sense'.

I claim as my invention:

1. The combination with a motorgenera tor set, of a main source of power, an auxiliary source of power, means for connecting' the generator across the auxiliary source of power to operate the generator as a motor, and means sensitive to the flow of current in the generator disposed to connect the motor across the main source of power when it rotates at a predetermined speed.

2. A control system :tor a motor-generatory set comprising a main source ot power, an auxiliary source of power, means for connecting the generator across the auxiliary source of power to operate it as a motor, and means sensitive to the iow of current in the generator disposed to connect the motor 'across the main source of power when it rotates at a predetermined speed, the energization of said motor connect-ing means being dependent upon the speed ot' the generator operating as a` motor.

3. A control .system for a motor-generator set comprising, in combination, a main source of power, an auxiliary source ofipower, means for connecting the generator across ineansfiior connectiiig` the generator across the auxiliary source ofpower to operate'it as f a'niotor, and a relay operable to connect,

the motor across the main source'ot' power when it rotates at a predetermined speed, said relay being provided with a plurality of windings adapted for diiterential ener- 'gization when the generator is operated as a motor from .said auxiliary source of power and cumulative energization when the` generator is operated by the motor.

5. A control system for a motor-generator set comprising, in combination, a main source of power, an auxiliary source of power,`

means for connecting the generator across the auxiliary source of power to operate it as a motor, a relay operable to connect the motor across the main source of power when it rotates at a predetermined speed, said relay being disposed Vtor continually increasing energization as the counteielfectroinotive force ot the. generator operated as a motor increases, said relay being adapted to connect the motor across the main source of power when said set rotates at a predetermined speed.

6. A control system for a motor-generator set comprising, in combination, a main source of power, an auxiliary source of power, means for yconnecting the generator across the auxiliary source of power to operate it as a motor, and a relay operable to connect the motor across the main source of power when it rotates at a predetermined speed, said relay being provided with a seriescoil and a shuntl coil, said series coil being disposed to oppose the shunt coil when the generator operates as a motor and to aid said shunt coil when the generator is driven by the motor.

7. A control system for a motor-generator setcomprising, in combination, a main source of power, an auxiliary source of power, means for connecting thevgenerator across the auxiliary source of power to operate it as a motor, a relay operable to connect the motor across the main source of power when it rotates at a predetermined speed, said relay being provided with a series coil and a shunt coil, said series coil being disposed to oppose the shuntcoil when the generator operates as a motor and to aid said shunt coil when the generator is driven by the motor, a resistance unit and means cooperative with said relay to effect the connection of the resistance unit in series relation with said shunt. coil.

8. In a control system, in combination, a motor-generator set, a main source of power for normally operating the motor, an auxiliary source of power, means for connecting the generator across the auxiliary source of power to operate it as a motor and means sensitive to the flow of current in the generator disposed to close automatically` the motor circuit when the motor rotates at a predetermined speed, said circuit-closing means being connected for energization by the generator when Vthe motor circuit is closed. y l

9. The combination .with a motor-generator set, of a main source of power, an auxiliary source of power, means for connect? ing the generator across the auxiliary source of (power to operate the generator as a motor an means responsive to changes in current in the generatorl disposed to connect automatically the motor across the main source` of power when it rotates at a predetermined speed.

In testimony whereof, I have hereunto subscribed my name this 22nd day of May, 1925.

WALTER H. SMITH. 

